Need Residential Retaining Wall Ideas
Need Residential Retaining Wall Ideas
(OP)
Hello. My property currently has a failing wood-tie multi-tier retaining wall on a slope that needs replacing ASAP. I did much searching and research and have come across many ideas but am looking for guidance on which to go with. COST is a BIG concern, however I want to replace this wall and not have to worry about it ever again...or at least 30 yrs.
Please give me some thoughts...
Current wall to replace is about 1200sqft face total. Three walls each roughly 4 feet high by 100 feet long. They vary in distance from eachother and towards one end, they begin to get closer to eachother then finally curve into eachother and finish off the last 25 feet as one high wall holding back the corner of my side/back yard.
New Ideas were:
1. pumping in concrete to make a single concrete wall about 10 ft high a few feet down the slope from the existing walls, then filling in and grading the property down to this new wall height.
2. three (or two) new tiered modular block walls with geogrid, such as Keystone, Anchor, Unilock or similar.
3. These "Green Walls" "Vegetated Walls" or "GeoWeb" such as the stacked bags or the block that has a large batter that is filled with dirt and plant seeds. This would either be tiered as well or just make one large slope.
I would probably need a fence for the slope idea, or a wall over 5 feet high, so that would need to be factored in to the cost. I did searches and am coming across prices from $20 to $60/sqft.
If someone recommends the Green Wall or Slope idea... I can't seem to find this product in my area?? (I'm in the New York Metro area).
Any help would be greatly appreciated! I am on a budget of about $40k MAX and am hoping for it to be much less than that. Thanks.
Ken
Please give me some thoughts...
Current wall to replace is about 1200sqft face total. Three walls each roughly 4 feet high by 100 feet long. They vary in distance from eachother and towards one end, they begin to get closer to eachother then finally curve into eachother and finish off the last 25 feet as one high wall holding back the corner of my side/back yard.
New Ideas were:
1. pumping in concrete to make a single concrete wall about 10 ft high a few feet down the slope from the existing walls, then filling in and grading the property down to this new wall height.
2. three (or two) new tiered modular block walls with geogrid, such as Keystone, Anchor, Unilock or similar.
3. These "Green Walls" "Vegetated Walls" or "GeoWeb" such as the stacked bags or the block that has a large batter that is filled with dirt and plant seeds. This would either be tiered as well or just make one large slope.
I would probably need a fence for the slope idea, or a wall over 5 feet high, so that would need to be factored in to the cost. I did searches and am coming across prices from $20 to $60/sqft.
If someone recommends the Green Wall or Slope idea... I can't seem to find this product in my area?? (I'm in the New York Metro area).
Any help would be greatly appreciated! I am on a budget of about $40k MAX and am hoping for it to be much less than that. Thanks.
Ken





RE: Need Residential Retaining Wall Ideas
www.PeirceEngineering.com
RE: Need Residential Retaining Wall Ideas
I looked into something similar, some contractors call it "Mafia Blocks" but I don't think I can get a machine in there to carry these in. Can a bobcat carry these in to the back yard?
Any thoughts on the total $/sqft to use this product?
thanks! Any other suggestions?
RE: Need Residential Retaining Wall Ideas
Attached as an example is a data sheet for these blocks as available from a Philadelphia area concrete supplier.
I have designed a few of these wall, usually for temporary use, but I don't have an installed price. The price would greatly depend on your available access. It may be easier to set the blocks with a hydraulic crane (picker).
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RE: Need Residential Retaining Wall Ideas
RE: Need Residential Retaining Wall Ideas
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RE: Need Residential Retaining Wall Ideas
RE: Need Residential Retaining Wall Ideas
Ron, If I did replace the walls with the segmented block at 4' high I will need to do the three tiers again. I was reading up on this stuff and some articles mention "global ??" which I believe has something to do with looking at the whole area to determine the structural requirements. This three-tier wall would only be 4' each one, however it is built on a fairly steep slope... the ground in front of the lowest wall will not be flat approaching the base of the wall. This makes a difference, correct? Also, I read the walls need to be minimum 2x the height stepped back from each other. Geogrid, I believe, may be needed in this case. Any thoughts?
RE: Need Residential Retaining Wall Ideas
Ron is correct that walls with smaller segmental blocks would look nice and are easier to handle, but the design height of a wall also includes the portion of the wall that is buried below the finished grade in front of the wall, usually at least the height of one block. Therefore, a 4' high wall without geogrids may really be only 3'-4" or less in exposed height. With bigger blocks, you can go higher without geogrids. Without geogrids, you could have less excavation (i.e. gouging into the hillside and disturbing the existing walls), less backfill, and probably no temporary sheeting.
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RE: Need Residential Retaining Wall Ideas
RE: Need Residential Retaining Wall Ideas
any suggestions from this forum seem to make no sense until we see a cross section that extends to either side of this "wall" by a distance of 20 ft or so. Also, it'd help to know the soil type.
I think if you have a failing timber wall (i.e., one that worked for a while and then "failed"), you could expect a similar design life if you just redid what you have. Whether you use block or timber would make little difference. If you want a better performance, it'd be good to know what happened. It sounds like you are the victim of failed cohesion and a wall that was stable only when the soil's cohesion was there to assist. I'm thinking you have some clay on either side of your wall and forming your slope. I'm thinking you need some mechanical stabilization (i.e., geotextile) to reconstruct your wall.
f-d
¡papá gordo ain't no madre flaca!
RE: Need Residential Retaining Wall Ideas
fattdad is correct. More information is needed to make a proper decision. For now, we're just throwing out ideas.
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RE: Need Residential Retaining Wall Ideas
You are willing to spend $40k and perhaps have a landscaper design it? How long will it last? Will you be willing to spend another $40k in 3 years when it fails?
RE: Need Residential Retaining Wall Ideas
No way!...I wouldn't leave this up to a landscaper to design. I am a PE and am getting ideas from here and my own research and am going to come up with some type of design and then review with a civil engineer for final review and stamp.
PEinc,
I like your big block in front of the existing wall idea but am questioning this... The bottom wall can be built in front of the old wall, but the second tier would wind up on top of or close to the old first tier wood wall. I'm thinking this old wood will eventually rot and create a weak base for the very heavy new wall above it. I don't know if that will work.
RE: Need Residential Retaining Wall Ideas
Materials testing labs readily have to discard tested concrete cylinders.
The original owner of Milwaukee Testing built some nice walls at his house using these cylinders. The last I knew they still stood.
Where I used to work we had many a homeowner coming by to take our tested cylinders,since we did not break them, once they started to yield.
Otherwise the labs have to dispose of them.
RE: Need Residential Retaining Wall Ideas
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RE: Need Residential Retaining Wall Ideas
RE: Need Residential Retaining Wall Ideas
I'm not a geotech, but I've designed (grading plans for) numerous tiered retaining wall. From my experience, there's a big difference in retaining wall design if it's for a fill slope or cut slope. When you have a tiered retaining wall holding up a fill slope (as example, this can be done at the lower portion of someone's front yard, to extend the flat area of yard), you usually do not have to consider reinforcement (geotextile) behind these walls.
But when you "cut" into an existing hill and try to use a tiered retaining wall to hold up this cut slope, geotextile/geogrid is almost always required. In order to avoid additional excavation for the geogrid, very often soil nails are used for reinforcement.
I think this may be why you are getting contradicting statements on whether you need reinforcement or not - it depends on if it's holding up a hill, or a flat area of fill. It sounds like from your description that you are trying to retain a hill. As previously stated, having a cross section of the existing conditions and soil types would certainly help.
The use of the large retaining wall blocks could help you avoid reinforcement, but I agree with the construction issues you mentioned above if you attempt to keep the existing walls in place.
I think it's prudent that you are trying to do a lot of this work by yourself (and with some minimal input from this forum). But, I would recommend that you pay a good local geotech/structural engineer for a few hours of time - you may be surprised how quickly they can determine the most cost-effective design for your situation. Just make sure you give them some site photos, soil types (if you can dig some holes and take photos), and an existing cross-section.
RE: Need Residential Retaining Wall Ideas
The discussion of the need for grids in this thread is based on the actual height(s) of the tiers, the available bench widths (1x, 2x, etc.), and the choice of small blocks vs. big blocks. For tiered wall on an existing hill, installation of grids would most likely be more involved and expensive than no grids.
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RE: Need Residential Retaining Wall Ideas
I understand it does not determine the need for geogrids, but holding up a flat fill or a steep grade directly correlates with two of the design items listed: slope stability and grading behind wall. So actually, where you are placing the wall has a lot to do with the need for geogrid.
RE: Need Residential Retaining Wall Ideas
Thanks for all the responses on this topic. I can't find an engineer in my area! I found one person but he is an over-designer and said he will only consider a reinforced concrete wall that would cost $150k to build... I don't consider someone like this an engineer. Anyone can design a wall that won't fail. An engineer can design a wall that will work yet be cost effective and sensible.
RE: Need Residential Retaining Wall Ideas
Two other comments:
1. "But when you "cut" into an existing hill and try to use a tiered retaining wall to hold up this cut slope, geotextile/geogrid is almost always required." So is temporary sheeting. Then, you are building two walls - one temporary and one permanent = expensive.
2. "In order to avoid additional excavation for the geogrid, very often soil nails are used for reinforcement." When this happens, you have not built an MSE wall. You have built a soil nail wall with an additional segmental block facade.
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RE: Need Residential Retaining Wall Ideas
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RE: Need Residential Retaining Wall Ideas
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RE: Need Residential Retaining Wall Ideas
RE: Need Residential Retaining Wall Ideas
Gabions are a possibility and desirable if you have access issues. However, while my past experience with gabion failures could be based on poor construction, I have seen a lot of these walls fall apart over time (bigger rocks tear through facing or smaller rocks get pushed out, creating voids, and settling occurs). Gabions walls don't necessarily "fail," but can be aesthetically unpleasing.
The use for "Redi-Rock" blocks was mentioned above as a possible replacement for the timber wall. But rather than tiering these walls, have you thought about the possibility of installing one 6'-8' high Redi-Rock wall in front of the first (existing) wall and backfilling behind this wall at a 3:1 or 4:1 slope? The height of RR wall and slope behind the wall will be based on existing wall batter. Plan on removing the existing wood timber wall before backfilling. The cost-effectiveness of this alternative will be greatly dependent on the cost to haul backfill material to your site. Another positive consideration is that (I believe) Redi-Rock will provide you with a certified ret. wall design (incl. global stability), so you can avoid using your local structural "engineer."
RE: Need Residential Retaining Wall Ideas
A lot of problem projects I have seen have someone who decided to build a retaining wall that holds up a side of the mountain and house at the top, but the footings aren't deep enough to make this wall do anything and no one ever desgined the wall before building. I would also suggest using someone familiar with the codes in your area to design a cost effective wall.
You should post a picture or sketch of the yard.
Civil Development Group, LLC
Los Angeles Civil Engineering specializing in Hillside Grading
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RE: Need Residential Retaining Wall Ideas
Civil Development Group, LLC
Los Angeles Civil Engineering specializing in Hillside Grading
http://www.civildevelopmentgroup.com
http://www.civildevelopmentgroup.com/blog
RE: Need Residential Retaining Wall Ideas
If you're hard up for fill dirt, pull all the walls out, grade flatter, like 4:1 or so up the hill a bit, then put your taller redi-rock wall in, then go 3:1 to the top of slope. That way you get some cut down that the bottom that you can use for fill at the top. Design your wall height, wall location, cut slope, and fill slope around what makes your cut and fill quantities work, so you don't have to bring in or haul off dirt.
In fact, that cut/fill analysis would be a fun exercise in basic civil engineering for you to toy with, xjken. Google the terms "shrink" and "swell" first. That should be fun stuff to get you started.
Good luck!
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Need Residential Retaining Wall Ideas
design engineer.what's more the cost of it is very litter, if you make a right products.
And i don't agree with some persons, because the geogrids is not very expensive even if you need the tanser's quality.
gengnan1@gmail.com
RE: Need Residential Retaining Wall Ideas
I attached a pic of the existing conditions as someone suggested above.
RE: Need Residential Retaining Wall Ideas
Just goes to show how "permanent" a landscape timber wall really is. I have one in my yard - the carpenter ants have now overcome whatever cheap pressure treating was used in the timbers.
Retaining walls need to be made of an inert, inorganic material to last. They get especially difficult to rebuild when those little trees that were planted when it was built have now grown to substantial size.
Ralph
Structures Consulting
Northeast USA
RE: Need Residential Retaining Wall Ideas
Redi-Rock: big and pretty but expensive to install. 12 feet tall will work without grid with the 60" base IF everything is level on top and bottom. A "bobcat" will have trouble moving these. Installed cost $35-$40 per square feet. They are very proud of their blocks.
Modular block: quick and easy. Design build contractors will handle the design and permits. Installed around $14-$18 per square feet.
Welded wire form slopes: Cheapest. A vegetated slope at 0.33:1 vertical batter will be ideal for your situation and again, a design build contractor will handle this for around $12-16$ installed.
Keep in mind these are for the facing, reinforcement and backfill placement. It will not include the backfill material or demo/excavation. Please don't even use the L word (landscape architect)when it comes to structural retaining walls. I have rebuilt dozens of walls "designed" by landscapers. I would shy away from the reclaimed concrete blocks due to the cold joints and inconsistent construction.